Low-power devices can be equipped with a power supply that converts an external source of energy into electric power. For example, a solar cell (or photovoltaic, PV, cell), a thermo-electrical generator, or a dynamo can be used for this purpose. The device can also be equipped with an energy harvesting controller that controls how the electric energy is collected from the power supply. Since the amount of energy provided by the external source of energy may be not be continuously sufficient to supply the demand of the device, the harvesting controller can be configured to store the harvested energy in a storage element. A backup battery can be provided in addition to the storage element, to take over power supply when the storage element is empty. The controller may thus be configured so that a storage element (such as a capacitor or rechargeable battery) is charged from one or more alternative energy sources, such as a PV-cell. As soon as the voltage of the storage element is high enough, the storage element is connected to the output by the controller (herein, the output is the actual application that consumes the generated electric power: for instance a Bluetooth-LE transceiver). The backup battery complements the storage element in small, low-power, applications.
During longer periods without available power from the alternative energy source(s), the storage element will be drained by the load and will eventually become too low in voltage to properly supply the load. Before this happens, the controller disconnects the output from the storage element and connects the output to a backup-battery, which may be a non-rechargeable battery. This ensures that the load is properly supplied under all conditions.
FIG. 1 illustrates an example power supply circuit. The circuit comprises an alternative energy supply 1, such as a photovoltaic cell, which is connected to a storage element 2 for storing the energy harvested from the alternative energy supply 1. The circuit also comprises a backup battery 3, and a load 4. The load 4 is a circuit that can consume the energy from the alternative energy supply 1, the storage element 2, and the backup battery 3. To this end, the load 4 is connected to output terminal 13 of the power supply circuit. If the alternative energy supply 1 and/or the storage element 2 have sufficient voltage, then switch 8 connects these sources 1,2 to the output terminal 13, and thus to the load 4. Otherwise, switch 9 connects the backup battery 3 to the output terminal 13. This is accomplished by the power supply circuit comprising comparator 5, inverting amplifier 6, amplifier 7, and switches 8 and 9. The charger 11 forms an interface between the alternative energy supply 1 and the storage element 2. The charger can be implemented as a DCDC converter, for example.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.